Chromogenic compounds, a process for their preparation and their use

ABSTRACT

Chromogenic compounds of the formula I ##STR1## and a process for their preparation are described, X denoting a hydrogen atom, a protective group customarily used in peptide chemistry or a group which irreversibly blocks the terminal amino group, 
     A and P being identical or different and denoting an alpha-, beta- or gamma-amino acid which is composed of 2 to 15 carbon atoms with up to 3 nitrogen atoms, 2 sulfur atoms and 6 oxygen atoms, the side-chain of which can be substituted, and P also denoting a dipeptide formed from amino acids of these types, 
     B denoting arginine, homoarginine, lysine, homolysine, ornithine or histidine and 
     R denoting a substituent in the 2- or 3-position. 
     The compounds can be used as substrates for the direction and the quantitative determination of hydrolytic enzymes of enzyme class 3.4.21.

This application is a continuation of application Ser. No. 06/691,867, filed Jan. 16, 1985, now abandoned, which is a division of application Ser. No. 06/554,942 filed Nov. 25, 1983, now U.S. Pat. No. 4,508,644.

The invention relates to chromogenic compounds of the general formula I ##STR2## their acid addition salts and a process for their preparation.

In the formula,

X denotes a hydrogen atom, a protective group customarily used in peptide chemistry or a group which irreversibly blocks the terminal amino group;

A and P are identical or different and denote an alpha-, beta- or gamma-amino acid which is composed of 2 to 15 carbon atoms with up to 3 nitrogen atoms, 2 sulfur atoms and 6 oxygen atoms, the side-chain of which can be substituted, and P also denotes a dipeptide formed from amino acids of these types;

B denotes arginine, homoarginine, lysine, homolysine, ornithine or histidine;

R denotes a substituent in the 2- or 3-position.

The invention also relates to use of these compounds as substrates for the detection and the quantitative determination of hydrolytic enzymes of enzyme class 3.4.21.

Chromogenic compounds for the determination of proteases are disclosed in German Offenlegungsschriften 2,527,932, 2,552,570, 2,629,067, 2,436,543, and 2,629,198 and the published European Patent Application 0,019,589 and 0,034,122.

These substrates used for the determination of proteases according to the state of the art have, however, considerable deficiencies in respect of their specificity. Thus, for example, the chromogenic substrates such as Tos-Gly-Pro-Arg-pNA (for abbreviations see later) and H-D-Phe-Pip-Arg-pNA, used for determining thrombin, are cleaved to a considerable extent by other proteases of the coagulation aand fibrinolysis cascade, such as plasma kallikrein, factor XII a (M 28,000 from placenta), plasmin and factor X a, as well as by trypsin and urokinase. Similar findings in respect of their substrate/enzyme non-specificity have emerged for chromogenic compounds as are commercially available for other proteases, such as plasma kallikrein, plasmin, factor X a and urokinase. The substrates having increased enzyme specificity, according to German Offenlegungsschrift 2,436,543, have the disadvantage that, after cleavage by the particular enzyme, they require, for subsequent liberation of the chromophore, an auxiliary enzyme acting as an aminopeptidase.

The object of this invention is to produce chromogenic compounds which have higher enzyme specificity and can be used without auxiliary enzymes.

The invention relates to compounds of the general formula I and the abovementioned definitions with the following explanations:

    ______________________________________                                         Ac       acetyl                                                                Ala      alanine                                                               βAla                                                                               beta-alanine                                                          ANBA     5-amino-2-nitrobenzoic acid                                           Arg      arginine                                                              Asn      asparagine                                                            Asp      aspartic acid                                                         Boc      t-butyloxycarbonyl                                                    But      aminobutyric acid                                                     γ-but                                                                             gamma-aminobutyric acid                                               Bz       benzoyl                                                               Bzl      benzyl                                                                CHA      cyclohexylalanine                                                     Cys      cysteine                                                              DCCI     dicyclohexylcarbodiimide                                              DCU      dicyclohexylurea                                                      Ddm      4,4'-dimethoxybenzhydryl                                              DMF      dimethylformamide                                                     EA       ethyl acetate                                                         Gln      glutamine                                                             Glu      glutamic acid                                                         Gly      glycine                                                               HAc      acetic acid                                                           His      histidine                                                             HOBt     hydroxybenzotriazole                                                  Ile      isoleucine                                                            Leu      leucine                                                               Lys      lysine                                                                Me       methyl                                                                Met      methionine                                                            MM       molecular mass                                                        Msc      methylsulfoethyloxycarbonyl                                           NMM      N--methylmorpholine                                                   Orn      ornithine                                                             PE       petroleum ether                                                       Pip      pipecolic acid                                                        pNA      para-nitroaniline (4-nitroaniline)                                    Pro      proline                                                               Pyr      pyroglutamic acid                                                     Ser      serine                                                                RT       room temperature                                                      tBu      tert.-butyl                                                           TCP      2,4,5-trichlorophenyl                                                 Thr      threonine                                                             TDM      4,4'-bis(dimethylamino)diphenylmethane                                Tos      toluenesulfonyl                                                       Tyr      tyrosine                                                              Val      valine                                                                Z        benzyloxycarbonyl                                                     ZTE      benzyloxycarbonylamino-2,2,2-trifluoroethyl.                          ______________________________________                                    

Unless otherwise noted, the amino acids are in the L form.

Within the scope of the invention, the term amino acid always denotes an alpha-, beta- or gamma-amino acid, which is composed of 2 to 15 carbon atoms with up to 3 nitrogen atoms, 2 sulfur atoms and 6 oxygen atoms.

If A is a chiral amino acid, then it is preferably in the D form when X is a hydrogen atom.

If P contains chiral amino acids, they can be in the D or L configuration.

The amino acids defined under A and P are not restricted to those which occur in natural proteins or peptide antibiotics. Other amino acids, such as pipecolic acid, cyclohexylalanine, azetidinecarboxylic acid, cysteic acid, 1-aminocyclohexylcarboxylic acid, phenylglycine or diphenylglycine are also suitable.

R can contain an ether, ester, amide, thioester or araliphatic bond, via which it can be bonded to the aromatic nucleus. The substituent is composed of 1 to 30 carbon atoms, it being possible for 1 to 10 carbon atoms to be replaced by oxygen, nitrogen or sulfur. Likewise, 2 to 10 hydrogen atoms can be replaced by elements, such as oxygen or sulfur.

The invention particularly relates to chromogenic compounds of the general formula II ##STR3## and their acid additional salts.

In the general formula II,

X denotes a hydrogen atom, a protective group customarily used in peptide chemistry or a group which irreversibly blocks the terminal amino group.

Protective groups customarily used in peptide chemistry are, for example, those according to E. Wunsch in Houben-Weyl, Volume XV/1, and the Peptides, Vol. 3, "Protection of Functional Groups in Peptide Synthesis", Academic Press 1981. Benzyloxycarbonyl, tert-butyloxycarbonyl, adamantyloxycarbonyl, methylsulfoethyloxycarbonyl and 9-fluororenylmethyloxycarbonyl are preferably used. A group which irreversibly blocks can be an acyl or sulfonyl group, preferably a R₄ --CO group, in which R₄ denotes an aliphatic hydrocarbon radical having 1-6 carbon atoms which can be substituted with 1-3 halogen atoms, or an alkaryl group having 6-10 carbon atoms, or can be a benzenesulfonyl or alkarylsulfonyl group having 7-10 carbon atoms, but particularly formyl, acetyl, benzoyl, trifluoroacetyl, toluenesulfonyl, mesyl, methoxybenzenesulfonyl, succinoyl or maleoyl;

A denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group comprising Ala, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Pyr, Thr, Tyr and Val;

C denotes a bond or an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group comprising Ala, Asp, Glu, Gly, Leu, Lys, Ser and Val;

D denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group comprising Ala, Asp, Glu, Gly, His, Leu, Phe, Pip, Pro, Ser, Thr, Tyr and Val;

B denotes L-arginine, L-homoarginine, L-lysine, L-homolysine, L-ornithine or L-histidine;

R preferably denotes COOR₁, CONR₂ R₃, CONH--(CH₂)_(n) --N(CH₃)₂, CO--Y--OR₁ and CO--Y--NR₂ R₃ in the 3-position of OR₁ in the 2-position of the 4-nitroaniline. Another substituent can be present in addition to R.

R₁ is an aliphatic hydrocarbon radical having 1 to 6 carbon atoms, an aromatic hydrocarbon radical having 6 or 10 carbon atoms, an araliphatic hydrocarbon radical having 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms;

R₂ is a hydrogen atom or a radical defined under R₁ ;

R₃ is an aliphatic hydrocarbon radical having 1 to 10 carbon atoms, an aromatic hydrocarbon radical having 6 or 10 carbon atoms, an araliphatic hydrocarbon radical having 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms;

Y denotes an alpha-, beta- or gamma-amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group comprising Ala, Asn, Asp, β-Ala, γ-But, Cys, Glu, Gly, Ile, Leu, Lys, Met, Arg, Phe, Pro, Ser, Thr, Tyr and Val;

n denotes 1 to 10.

Suitable side-chain groups of the amino acids corresponding to A, C, D and Y are carboxyl, hydroxyl, mercapto, imidazole, amino and amide groups. According to their reactivity, these can be substituted by the protective groups customarily used in peptide chemistry.

4,4'-Dimethoxybenzhydryl and 4,4'-dimethylbenzhydryl are preferably used to protect the amide group in Gln and Asn. Benzyloxycarbonylamino-2,2,2-trifluoroethyl (ZTE), tert.-butyloxycarbonyl and tosyl are preferably used to protect the imidazole group in His. To protect the guanidino group in arginine, it can be protonated or substituted by N^(G) -tosyl, N^(G) -nitro, N^(G) -adamantyloxycarbonyl and N^(G) -benzyloxycarbonyl. Benzyloxycarbonyl, tert.-butoxyloxycarbonyl, methylsulfoethyloxycarbonyl or tosyl are preferably used to protect the ε-amino group of lysine. Esterification with aliphatic, aromatic or araliphatic alcohols, such as, for example, methanol, tert.-butanol, phenol and benzyl alcohol, are preferably used to protect the carboxyl group in Asp and Glu. The SH group in cysteine is preferably protected as the S-benzyl or S-alkylsulfenyl. The preferred protection suitable for the hydroxyl group in tyrosine, serine and threonine is esterification with benzyl or t-butyl.

The novelty of the substrates according to the invention lies in the derivatization of the p-nitroanilide group. The spectrophotometric properties of the new derivatives differ either not at all or only insignificantly from those of 4-nitroaniline.

The disadvantage of non-specificity on use as enzyme substrates is exhibited by the new compounds according to the invention either not at all or to a considerably lesser extent than by the substrates of the state of the art. The new substrates are distinguished by derivatization of the chromogenic group, in this case 4-nitroaniline. The space occupied by the chromophore undergoes great changes on introduction of different substituents. This leads to a considerable increase in specificity for certain enzymes, particularly for thrombin, plasmin, kallikrein, factor X a, urokinase and C₁ -esterase.

The invention also relates to a process for the preparation of a compound of the formula I, which comprises condensing a peptide derivative of the general formula III

    X--A--P--OH                                                (III)

in which

X, A and P have the abovementioned meanings, and OH is a hydroxyl group, X not, however, denoting a hydrogen atom, and additional functional groups in the amino acid side-chains being substituted with protective groups,

with an amino acid derivative of the general formula IV ##STR4## in which B has the abovementioned meaning, but additional functional groups in the side-chain of the amino acid being substituted by protective groups and R having the definition given for general formula I.

The protective groups are, where appropriate, then split off.

The methods customarily used for condensation in peptide chemistry are used, for example, the azide method, the method using mixed anhydrides, or the methods using activated esters (trichlorophenyl ester, pentachlorophenyl ester, hydroxysuccinimide ester or nitrophenyl ester). The carbodiimide process is preferably used, optionally with the addition of hydroxybenzotriazole in accordance with Chem. Ber. 103, 788 (1970).

The 5-amino-2-nitrobenzoic acid derivatives (ANBA derivatives) according to the invention are accessible by known esterification and amide-forming reactions. An advantageous means of preparing the ANBA esters is the acid chloride method using thionyl chloride, phosphorus trichloride or phosphorus pentachloride. Thionyl chloride is preferably used with the appropriate alcohol. The ANBA esters are generally soluble in chloroform or ethyl acetate.

An advantageous means of preparing the ANBA amides, ANBA-amino acid esters, ANBA-amino acid amides and ANBA dimethylaminoalkylamides is condensation by methods customarily used in peptide chemistry, for example the method using mixed anhydrides, the acid chloride process or the carbodiimide method. The carbodiimide process is preferably used, with the addition of hydroxybenzotriazole. Only some of the products are soluble in ethyl acetate, but they can frequently be purified by recrystallization from it. No protective group for the free amino group in ANBA is necessary.

The reaction of the ANBA derivatives with one of the amino acids designated B in the general formula I can take place via the isocyanate of the ANBA derivative. Likewise, the amino acid derivative can be activated using the azide method or the phosphorus oxychloride method. The phosphorus oxychloride method is preferably used. All functional groups, apart from the carboxyl group, of the amino acids should be blocked using the protective groups customarily used in peptide chemistry. It is possible to protect the guanidino group of arginine by protonating it.

The invention also relates to the use of the compounds according to the invention for the detection and for the examination of proteinases. The bond between B and the 4-nitroanilide derivative is cleaved by the action of a proteinase, this giving rise to a chromophoric nitroanilide derivative which can be measured photometrically.

The invention particularly relates to the use of the compounds of the general formula I for the detection and for the determination of enzymes.

The procedure for the determination of a hydrolytic enzyme comprises adding a compound corresponding to formula I to the solution in which the enzyme is to be determined, and measuring the amount or the rate of formation of the nitroaniline derivative which has been split off, these being direct measures of the activity of the hydrolytic enzyme.

Examples of compounds according to the invention, the starting compounds for the corresponding two formulae III and IV and the final reaction steps (for numbers, see "Preparation of the new compounds" after Table IX) are listed in the Table I below. The peptide derivatives according to formula III were prepared by known processes of preparation according to E. Wunsch in Houben-Weyl, Volume XV/1+2 and The Peptides, Vol. 1, "Major Methods of Peptide Bond Formation", Academic Press 1979. The preparation of the chromogenic amino acid derivatives of the general formula IV is described below.

All new compounds have been characterized by elemental analysis, amino acid analysis and thin-layer chromatography. The chemical purity was demonstrated by thin-layer chromatography in various solvent mixtures. Racemization was checked by gas chromatography in a glass capillary column coated with Chirasil-Val® according to J. Chromatogr. Sci. 15, 174 (1977), and was always below 2%.

                                      TABLE I                                      __________________________________________________________________________     Compound according to the                                                                              Starting substance corresponding                                                                         Last reaction                invention               to general formula III or IV                                                                             step                         __________________________________________________________________________     1  H--D-Val--Leu--Lys--ANBA methyl                                                                     Boc--D-Val--Leu--OH       6, 7b                           ester × 2HCl   H--Lys(Z)--ANBA methyl ester × HCl               2  H--D-Phe--Pro--Arg--ANBA methyl                                                                     Boc--D-Phe--Pro--OH       6, 7a                           ester                H--Arg--ANBA methyl ester × 2HCl                 3  Bz--Ile--Glu(OMe)--Gly--Arg--                                                                       Bz--Ile--Glu(OMe)--OH     6                               ANBA methyl ester × HCl                                                                       H--Gly--Arg--ANBA methyl ester × 2HCl            4  Boc--Leu--Ser--Thr--Arg--                                                                           Boc--Leu--Ser--Thr--OH    6                               ANBA methyl ester × HCl                                                                       H--Arg--ANBA methyl ester × 2HCl                 5  H--D-Leu--Val--Gly--Lys--                                                                           Boc--D-Leu--Val--Gly--OH  6, 7b                           ANBA methyl ester × 2HCl                                                                      H--Lys(Z)--ANBA methyl ester × HCl               6  H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           ethyl ester × 2HCl                                                                            H--Arg--ANBA ethyl ester × 2HCl                  7  Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               ethyl ester × HCl                                                                             H--Arg--ANBA ethyl ester × 2HCl                  8  Pyr--Gly--Arg--ANBA  Pyr--Gly--OH              6                               ethyl ester × HCl                                                                             H--Arg--ANBA ethyl ester × 2HCl                  9  H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           ethyl ester × 2HCl                                                                            H--Arg--ANBA ethyl ester × 2HCl                  10 H--D-Val--Asp--Arg--ANBA                                                                            Boc--D-Val--Asp(OtBu)--OH 6, 7a                           n-propyl ester × 2HCl                                                                         H--Arg--ANBA n-propyl ester × 2HCl               11 H--D-Phe--Tyr--Arg--ANBA                                                                            Boc--D-Phe--Tyr--OH       6, 7a                           n-propyl ester × 2HCl                                                                         H--Arg--ANBA n-propyl ester × 2HCl               12 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           isopropyl ester × 2HCl                                                                        H--Arg--ANBA isopropyl ester × 2HCl              13 H--D-Cys(sBzl)--Pro--Arg--                                                                          Boc--D-Cys(sBzl)--Pro--OH 6, 7a                           ANBA isopropyl ester × 2HCl                                                                   H--Arg--ANBA isopropyl ester × 2HCl              14 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           n-butylester × 2HCl                                                                           H--Arg--ANBA n-butyl ester × 2HCl                15 Z--D-Leu--Gly--Arg--ANBA                                                                            Z--D-Leu-- Gly--OH        6                               n-butyl ester × HCl                                                                           H--Arg--ANBA n-butyl ester × 2HCl                16 Pyr--Gly--Arg--ANBA  Pyr--Gly--OH              6                               n-butyl ester × HCl                                                                           H--Arg--ANBA n-butyl ester × 2HCl                17 H--D-Pro--Phe--Arg--ANBA                                                                            Boc--D-Pro--Phe--OH       6, 7a                           n-butyl ester × 2HCl                                                                          H--Arg--ANBA n-butyl ester × 2HCl                18 H--D-Val--Thr--Arg--ANBA                                                                            Boc--D-Val--Thr--OH       6, 7a                           isobutyl ester × 2HCl                                                                         H--arg--ANBA isobutyl ester × 2HCl               19 Msc--Gly--Ser--Lys--ANBA                                                                            Msc--Gly--Ser--OH         6, 7b                           t-butyl ester × HCl                                                                           H--Lys(Z)--ANBA t-butyl ester                          20 H--D-Phe--Tyr--Lys--ANBA                                                                            Boc--D-Phe--Tyr--OH       6, 7b                           n-pentyl ester × 2HCl                                                                         H--Lys(Z)--ANBA n-pentyl ester                         21 Bz--Ile--Glu(OMe)--Gly--Arg--                                                                       Bz--Ile--Glu(OMe)--OH     6                               ANBA n-penthyl ester × HCl                                                                    H--Gly--Arg--ANBA n-pentyl ester × 2HCl          22 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           2-pentyl ester × 2HCl                                                                         H--Arg--ANBA 2-pentyl ester                            23 H--D-Lys(Z)--Gly--Arg--ANBA                                                                         Boc--D-Lys(Z)--Gly--OH    6, 7a                           n-hexyl ester × 2HCl                                                                          H--Arg--ANBA n-hexyl ester × 2HCl                24 N--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           benzyl ester × 2HCl                                                                           H--Arg--ANBA benzyl ester × 2HCl                 25 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               benzyl ester × HCl                                                                            H--Arg--ANBA benzyl ester × 2HCl                 26 Z--D-Leu--Gly--Arg--ANBA                                                                            Z--D-Leu--Gly--OH         6                               benzyl ester × HCl                                                                            H--Arg--ANBA benzyl ester × 2HCl                 27 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           methylamide × 2HCl                                                                            H--Arg--ANBA methylamide × 2HCl                  28 H--D-Val--Leu--Lys--ANBA                                                                            Boc--D-Val--Leu--OH       6, 7b                           methylamide × 2HCl                                                                            H--Lys(Z)--ANBA methylamide × HCl                29 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               methylamide × Hcl                                                                             H--Arg--ANBA methylamide × 2HCl                  30 Z--D-Leu--Gly--Arg--ANBA                                                                            Z--D-Leu--Gly--OH         6                               methylamide × HCl                                                                             H--Arg--ANBA methylamide × 2HCl                  31 Bz--Ile--Glu(OMe)--Gly--Arg--                                                                       Bz--Ile--Glu(OMe)--OH     6                               ANBA methylamide × HCl                                                                        H--Gly--Arg--ANBA methylamide × 2HCl             32 Pyr--Gly--Arg--ANBA  Pyr--Gly--OH              6                               methylamide × HCl                                                                             H--Arg--ANBA methylamide × 2HCl                  33 H--D-Pro--Phe--Arg--ANBA                                                                            Boc--D-Pro--Phe--OH       6, 7a                           methylamide × 2HCl                                                                            H--Arg--ANBA methylamide × 2HCl                  34 H--D-Ala--Gly--Arg--ANBA                                                                            Boc--D-Ala--Gly--OH       6, 7a                           methylamide × 2HCl                                                                            H--Arg--ANBA methylamide × 2HCl                  35 H--D-Phe--Tyr--Arg--ANBA                                                                            Boc--D-Phe--Tyr--OH       6, 7a                           ethylamide × 2HCl                                                                             H--Arg--ANBA ethylamide × 2HCl                   36 Boc--His--(Boc)--Gly--Arg--ANBA                                                                     Boc--His--(Boc)--Gly--OH  6                               ethylamide × HCl                                                                              H--Arg--ANBA ethylamide × 2HCl                   37 H--D-Phe--Ser(OBzl)--Arg--ANBA                                                                      Boc--D-Phe--Ser(OBzl)--OH 6, 7a                           n-propylamide × 2HCl                                                                          H--Arg--ANBA n-propylamide × 2HCl                38 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           isopropylamide × 2HCl                                                                         H--Arg--ANBA isopropylamide × 2HCl               39 H--D-Val--Tyr(OBzl)--Arg--                                                                          Boc--D-Val--Tyr(OBzl)--OH 6, 7a                           ANBA isopropylamide × 2HCl                                                                    H--Arg--ANBA isopropylamide ×  2HCl              40 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               iropropylamide × HCl                                                                          H--Arg--ANBA isopropylamide × 2HCl               41 Z--D-Leu--Gly--Arg--ANBA                                                                            Z--D-Leu--Gly--OH         6                               isopropylamide × HCl                                                                          H--Arg--ANBA isopropylamide × 2HCl               42 Bz--Ile--Glu(OMe)--Gly--Arg--                                                                       Bz--Ile--Glu(OMe)--OH     6                               ANBA isopropylamide × HCl                                                                     H--Gly--Arg--ANBA isopropylamide × 2HCl          43 Pyr--Gly--Arg--ANBA  Pyr--Gly--OH              6                               isopropylamide × HCl                                                                          H--Arg--ANBA isopropylamide × 2HCl               44 H--D-Pro--Phe--Arg--ANBA                                                                            Boc--D-Pro--Phe--OH       6, 7a                           isopropylamide × 2HCl                                                                         H--Arg--ANBA isopropylamide × 2HCl               45 H--D-Phe--Pip--Arg--ANBA                                                                            Boc--D-Phe--Pip--OH       6, 7a                           isopropyamiide × 2HCl                                                                         H--Arg--ANBA isopropylamide × 2HCl               46 H--D-Glu--Gly--Leu--Arg--                                                                           Boc--D-Glu(OBzl)--Gly--Leu--OH                                                                           6, 7c                           ANBA isopropylamide × 2HCl                                                                    H--Arg--ANBA isopropylamide × 2HCl               47 H--D-Glu--Gly--Leu--Lys--ANBA                                                                       Boc--D-Glu(OBzl)--Gly--Leu--OH                                                                           6, 7c                           isopropylamide × 2HCl                                                                         H--Lys(Z)--ANBA isopropylamide × HCl             48 Bz--Ile--Asp-- Ala--Arg--                                                                           Bz--Ile--Asp(OtBu)--OH    6, 7a                           ANBA n-butylamide × HCl                                                                       H--Ala--Arg--ANBA n-butylamide × 2HCl            49 H--D-Phe--Tyr--Arg--ANBA                                                                            Boc--D-Phe--Tyr--OH       6, 7a                           t-butylamide × 2HCl                                                                           H--Arg--ANBA t-butylamide × 2HCl                 50 H--D-Leu--Val--Gly--Lys--                                                                           Boc--D-Leu--Val--Gly--OH  6, 7b                           ANBA isobutylamide × 2HCl                                                                     H--Lys(Z)--ANBA isobutylamide × HCl              51 H--D-Phe--Ser(OBzl)--                                                                               Boc--D-Phe--Ser(OBzl)--OH 6, 7b                           Orn--ANBA n-pentylamide × 2HCl                                                                H--Orn(Z)--ANBA n-pentylamide × HCl              52 H--D-Phe--Pro--His--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7b                           neopentylamide × 2HCl                                                                         H--His(ZTE)--ANBA neopentylamide × HCl           53 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           neopentylamide × 2HCl                                                                         H--Arg--ANBA neopentylamide × 2HCl               54 H--D-Val--Leu--Lys--ANBA                                                                            Boc--D-Val--Leu--OH       6, 7a                           neopentylamide × 2HCl                                                                         H--Lys(Z)--ANBA neopentylamide × HCl             55 Z--D-Val--Leu--Arg--ANBA                                                                            Z--D-Val--Leu--OH         6                               neopentylamide × HCl                                                                          H--Arg--ANBA neopentylamide × 2HCl               56 H--D-Phe--His(ZTE)--Arg--                                                                           Boc--D-Phe--His(ZTE)--OH  6, 7a                           ANBA neopentylamide × 2HCl                                                                    H--Arg--ANBA neopentylamide × 2HCl               57 H--D-Pro--Phe--Arg--ANBA                                                                            Boc--D-Pro--Phe--OH       6, 7a                           neopentylamide × 2HCl                                                                         H--Arg--ANBA neopentylamide × 2HCl               58 Tos--Val--Pro--Arg--ANBA                                                                            Tos--Val--Pro--OH         6                               n-hexylamide × HCl                                                                            H--Arg--ANBA n-hexylamide × 2HCl                 59 Tos--Gly--Val--Orn--ANBA                                                                            Tos--Gly--Val--OH         6, 7b                           n-octylamide × HCl                                                                            H--Orn(Z)--ANBA n-octylamide × HCl               60 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           n-decylamide × 2HCl                                                                           H--Arg--ANBA n-decylamide × 2HCl                 61 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           benzylamide × 2HCl                                                                            H--Arg--ANBA benzylamide × 2HCL                  62 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               benzylamide × HCl                                                                             H--Arg--ANBA benzylamide × 2HCl                  63 Z--D-Leu--Gly--Arg--ANBA                                                                            Z--D-Leu--Gly--OH         6                               benzylamide × HCl                                                                             H--Arg--ANBA benzylamide × 2HCl                  64 Bz--Ile--Glu(OMe)--Gly--Arg                                                                         Bz--Ile--Glu(OMe)--OH     6                               ANBA benzylamide ×  HCl                                                                       H--Gly--Arg--ANBA benzylamide × 2HCl             65 Pyr--Gly--Arg--ANBA  Pyr--Gly--OH              6                               benzylamide × HCl                                                                             H--Arg--ANBA benzylamide × 2HCl                  66 H--D-Pro--Phe--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           benzylamide × 2HCl                                                                            H--Arg--ANBA benzylamide × 2HCl                  67 Bz--Ile--Asp--Gly--Arg--ANBA                                                                        Bz--Ile--Asp(OtBu)--OH    6, 7a                           benzylamide × HCl                                                                             H--Gly--Arg--ANBA benzylamide × 2HCl             68 H--Gly--Val--Orn--ANBA                                                                              Z--Gly--Val--OH           6, 7b                           benzylamide × 2HCl                                                                            H--Orn(Z)--ANBA benzylamide × HCl                69 Ac--Phe--Glu(OtBu)--Arg--ANBA                                                                       Ac--Phe--Glu(OtBu)--OH    6                               phenethylamide × HCl                                                                          H--Arg--ANBA phenethylamide × 2HCl               70 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           phenethylamide × 2HCl                                                                         H--Arg--ANBA phenethylamide × 2HCl               71 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           phenethylamide × 2HCl                                                                         H--Arg--ANBA phenethylamide × 2HCl               72 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               cyclopentylamide × HCl                                                                        H--Arg--ANBA--cyclopentylamide × 2HCl            73 H-- D-Phe--Pro--Arg--ANBA                                                                           Boc--D-Phe--Pro--OH       6, 7a                           cyclohexylamide × 2HCl                                                                        H--Arg--ANBA cyclohexylamide × 2HCl              74 Ac--Phe--Glu(OtBu)--Arg--ANBA                                                                       Ac--Phe--Glu(OtBu)--OH    6                               cyclohexylamide × HCl                                                                         H--Arg--ANBA cyclohexylamide × 2HCl              75 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           diethylamide × 2HCl                                                                           H--Arg--ANBA diethylamide × 2HCl                 76 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               diisopropylamide × HCl                                                                        H--Arg--ANBA diisopropylamide × 2HCl             77 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           diisopropylamide × 2HCl                                                                       H--Arg--ANBA diisopropylamide × 2HCl             78 H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           dicyclohexylamide × 2HCl                                                                      H--Arg--ANBA dicyclohexylamide × 2HCl            79 H--D-Phe--His(ZTE)--Arg--ANBA                                                                       Boc--D-Phe--His(ZTE)--OH  6, 7a                           dimethylaminoethylamide × 3HCl                                                                H--Arg--ANBA dimethylaminoethylamide × 3HCl      80 H--D-Phe--Pro--Arg--ANBA dimethyl-                                                                  Boc--D-Phe--Pro--OH + H--Arg--ANBA                                                                       6, 7a                           aminopropylamide × 3HCl                                                                       dimethylaminopropylamide × 3HCl                  81 Bz--Ile--Glu(OMe)--Gly--Arg--ANBA                                                                   Bz--Ile-- Glu(OMe)--OH    6                               dimethylaminopropylamide × 2HCl                                                               H--Gly--Arg--ANBA dimethylaminopropylamide                                     ×                                                                        3HCl                                                   82 H--D-Phe--Pro--Arg--2-methoxy-pNA ×                                                           Boc--D-Phe--Pro--OH       6, 7a                           2HCl                 H--Arg--2-methoxy-pNA × 2HCl                     83 Ac--Phe--Glu(OtBu)--Arg--                                                                           Ac--Phe--Glu(OtBu)--OH    6                               2-methoxy-pNA × HCl                                                                           H--Arg--2-methoxy-pNA × 2HCl                     84 Z--D-Leu--Gly--Arg--2-methoxy                                                                       Z--D-Leu--Gly--OH         6                               pNA × HCl      H--Arg--2-methoxy-pNA × 2HCl                     85 Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               2-methoxy-pNA × HCl                                                                           H--Arg--2-methoxy-pNA × 2HCl                     86 Bz--Ile--Glu(OMe)--Gly--Arg                                                                         Bz--Ile--Glu(OMe)--OH     6                               2-methoxy-pNA × HCl                                                                           H--Gly--Arg--2-methoxy-pNA × 2HCl                87 Z--D-Val--Leu--Arg--2-                                                                              Z--D-Val--Leu--OH         6                               methoxy-pNA × HCl                                                                             H--Arg--2-methoxy-pNA × 2HCl                     88 H--D-Val--Leu--arg--2-                                                                              Z--D-Val--Leu--OH         6, 7b                           methoxy-pNA × HCl                                                                             H--Arg--2-methoxy-pNA × 2HCl                     89 Pyr--Gly--Arg--2-    Pyr--Gly--OH              6                               methoxy-pNA × HCl                                                                             H--Arg--2-methoxy-pNA × 2HCl                     90 H--D-Pro--Phe--Arg--2-                                                                              Boc--D-Pro--Phe--OH       6, 7a                           methoxy-pNA × 2HCl                                                                            H--Arg--2-methoxy-pNA × 2HCl                     91 Boc--D-Lys(Z)--Gly--Arg--                                                                           Boc--D-Lys(Z)--Gly--OH    6                               2-methoxy-pNA × HCl                                                                           H--Arg--2-methoxy-pNA × 2HCl                     92 H--D-Lys(Z)--Gly--Arg--                                                                             Boc--D-Lys(Z)--Gly--OH    6, 7a                           2-methoxy-pNA × 2HCl                                                                          H--Arg--2-methoxy-pNA × 2HCl                     93 Boc--D-Lys(Z)--Gly--Gly--Arg--                                                                      Boc--D-Lys(Z)--Gly--OH    6                               2-methoxy-pNA × HCl                                                                           H--Gly--Arg--2-methoxy-pNA × 2HCl                94 Bz--Ile--Asp--Ala--Arg--2-                                                                          Bz--Ile--Asp(OtBu)--OH    6, 7a                           methoxy-pNA × HCl                                                                             H--Arg--2-methoxy-pNA × 2HCl                     95 H--D-Thr--Ala--Thr--Arg--                                                                           Boc--D-Thr--Ala--Thr--OH  6, 7a                           2-methoxy-pNA × 2HCl                                                                          H--Arg--2-methoxy-pNA × 2HCl                     96 Boc--Leu--Ser--Thr--Arg--                                                                           Boc--Leu--Ser--Thr--OH    6                               2-methoxy-pNA × HCl                                                                           H--Arg--2-methoxy-pNA × 2HCl                     97 H--D-Phe--Pro--Arg--2-butoxy-                                                                       Boc--D-Phe--Pro--OH       6, 7a                           pNA × 2HCl     H--Arg--2-butoxy-pNA × 2HCl                      98 Pyr--Gly--Arg--2-butoxy                                                                             Pyr--Gly--OH              6                               pNA × HCl      H--Arg--2-butoxy-pNA ×  2HCl                     99 Z--D-Leu--Gly--Arg--2-                                                                              Z--D-Leu--Gly--OH         6                               butoxy-pNA × HCl                                                                              H--Arg--2-butoxy-pNA × 2HCl                      100                                                                               H--D-Val--Leu--Arg--2-                                                                              Z--D-Val--Leu--OH         6, 7b                           butoxy-pNA × 2HCl                                                                             H--Arg--2-butoxy-pNA × 2HCl                      101                                                                               H--D-Lys(Z)--Gly--Arg--                                                                             Boc--D-Lys(Z)--Gly--OH    6, 7a                           2-butoxy-pNA × 2HCl                                                                           H--Arg--2-butoxy-pNA × 2HCl                      102                                                                               Tos--Gly--Pro--Arg--ANBA                                                                            Tos--Gly--Pro--OH         6                               Gly methyl ester × HCl                                                                        H--Arg--ANBA--Gly methyl ester × 2HCl            103                                                                               H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           gly ethyl ester × 2HCl                                                                        H--Arg--ANBA--Gly methyl ester × 2HCl            104                                                                               Pyr--Gly--Arg--ANBA--Ala                                                                            Pyr--Gly--OH              6                               methyl ester × HCl                                                                            H--Arg--ANBA--Ala methyl ester × 2HCl            105                                                                               Boc--Leu--Ser--Thr--Arg--ANBA                                                                       Boc--Leu--Ser--Thr--Oh    6                               Ala methyl ester × HCl                                                                        H--Arg--ANBA--Ala methyl ester × 2HCl            106                                                                               H--D-Lys(Z)--Gly--Arg--ANBA                                                                         Boc--D-Lys(Z)--Gly--OH    6, 7a                           β-Ala ethyl ester × 2HCl                                                                 H-- Arg--ANBA--β-Ala ethyl ester ×                                  2HCl                                                   107                                                                               Tos--Gly--Pro--Arg--ANBA--Ala                                                                       Tos--Gly--Pro--OH         6                               ethyl ester × HCl                                                                             H--Arg--ANBA--Ala ethyl ester × 2HCl             108                                                                               H--D-Phe--Pro--Arg--ANBA--                                                                          Boc--D-Phe--Pro--OH       6, 7a                           γ-but ethyl ester × 2HCl                                                                H--Arg--ANBA--γ-but ethyl ester ×                                  2HCl                                                   109                                                                               H--D-Tyr--His(ZTE)--Arg--                                                                           Boc--D-Tyr--His(ZTE)--OH  6, 7a                           ANBA--γ-but ethyl ester × 2HCl                                                          H--Arg--ANBA--γ-but ethyl ester ×                                  2HCl                                                   110                                                                               H--D-Phe--Pro--Arg--ANBA                                                                            Boc--Arg--ANBA--γ-but ethyl ester ×                                2HCl                      6, 7a                           Val methyl ester × 2HCl                                                                       H--Arg--ANBA--Val methyl ester × 2HCl            111                                                                               Pyr--Gly--Arg--ANBA--Val                                                                            Pyr--Gly--OH              6                               methyl ester × HCl                                                                            H--Arg--ANBA--Val methyl ester × 2HCl            112                                                                               Z--D-Leu--Gly--Arg--ANBA--Leu                                                                       Z--D-Leu--Gly--OH         6                               methyl ester × HCl                                                                            H--Arg--ANBA--Leu methyl ester × 2HCl            113                                                                               H--D-Thr--Ala--Thr--Arg--ANBA                                                                       Boc--D-Thr--Ala--Thr--OH  6, 7a                           Ile methyl ester × 2HCl                                                                       H--Arg--ANBA--Ile methyl ester × 2HCl            114                                                                               H--D-Val--Lys--Val--Arg--ANBA--                                                                     Z--D-Val--Lys(Z)--Val--OH 6, 7b                           Ile methyl ester × 3HCl                                                                       H--Arg--ANBA--Ile methyl ester × 2HCl            115                                                                               H--D-Phe--Pro--ANBA--Ile                                                                            Boc--D-Phe--Pro--OH       6, 7a                           methyl ester × 2HCl                                                                           H--Arg--ANBA--Ile methyl ester × 2HCl            116                                                                               H--D-Phe--Tyr--Arg--ANBA--Pro                                                                       Boc--D-Phe--Tyr--OH       6, 7a                           methyl ester × 2HCl                                                                           H--Arg--ANBA--Pro methyl ester × 2HCl            117                                                                               Ac--Gln(Ddm)--Leu--Gly--Arg--                                                                       Hc--Gln(Ddm)--Leu--Gly--OH                                                                               6                               ANBA--Phe methyl ester × HCl                                                                  H--Arg--ANBA--Phe methyl ester × 2HCl            118                                                                               H--D-Phe--Pro--Arg--ANBA                                                                            Boc--D-Phe--Pro--OH       6, 7a                           Lys(Z) methyl ester × 2HCl                                                                    H--Arg--ANBA--Lys(Z) methyl ester × 2HCl         119                                                                               Boc--D-Lys(Z)--Gly--Arg--ANBA--                                                                     Boc--D-Lys(Z)--Gly--OH    6                               Lys(Z) methyl ester × HCl                                                                     H--Arg--ANBA--Lys(Z) methyl ester × 2HCl         120                                                                               H--D-Lys(Z)--Gly--Arg--ANBA--                                                                       Boc--D-Lys(Z)--Gly--OH    6, 7a                           Lys(Z) methyl ester × 2HCl                                                                    H--Arg--ANBA--Lys(Z) methyl ester × 2HCl         121                                                                               H--D-Phe--Pro--Arg--ANBA--Ser                                                                       Boc--D-Phe--Pro--OH       6, 7a                           methyl ester × 2HCl                                                                           H--Arg--ANBA--Ser methyl ester × 2HCl            122                                                                               H--D-Ala--Gly--Arg--ANBA--Thr                                                                       Boc--D-Ala--Gly--OH       6, 7a                           methyl ester × 2HCl                                                                           H--Arg--ANBA--Thr methyl ester × 2HCl            123                                                                               H--D-Tyr--His(ZTE)--Arg--ANBA                                                                       Boc--D-Tyr--His(ZTE)--OH  6, 7a                           Tyr methyl ester × 2HCl                                                                       H--Arg--ANBA--Tyr methyl ester × 2HCl            124                                                                               H--D-Phe--Pro--Arg--ANBA--Arg                                                                       Boc--D-Phe--Pro--OH       6, 7c                           methyl ester × 3HCl                                                                           H--Arg--ANBA--Arg(NO.sub.2) methyl ester ×                               2HCl                                                   125                                                                               H--D-Phe --Pro--Arg--ANBA--Glu                                                                      Boc--D-Phe--Pro--OH       6, 7a                           methyl ester × 2HCl                                                                           H--Arg--ANBA--Glu methyl ester × 2HCl            126                                                                               H--D-Val--Leu--Lys--ANBA--Asp                                                                       Z--D-Val--Leu--OH         6, 7b                           methyl ester × 2HCl                                                                           H--Lys(Z)--ANBA--Asp methyl ester × HCl          127                                                                               Pyr--Gly--Arg--ANBA--Cys                                                                            Pyr--Gly--OH              6                               methyl ester × H--Arg--ANBA--Cys methyl ester × 2HCl            128                                                                               H--D-Pro--Phe--Arg--ANBA--                                                                          Boc--D-Pro--Phe--OH       6, 7a                           met methyl ester × 2HCl                                                                       H--Arg--ANBA--Met methyl ester × 2HCl            129                                                                               H--D-Phe--Pro--Arg--ANBA--                                                                          Boc--D-Phe--Pro--OH       6, 7a                           Ala isopropylamide × 2HCl                                                                     H--Arg--ANBA--Ala isopropylamide × 2HCl          130                                                                               Z--D-Leu--Gly--Arg--ANBA--                                                                          Z--D-Leu--Gly--OH         6                               Ile methylamide × HCl                                                                         H--Arg--ANBA--Ile methylamide × 2HCl             131                                                                               H--D-Val--Tyr(OBzl)--Arg--ANBA--                                                                    Boc--D-Val--Tyr(OBzl)--OH 6, 7a                           Ile diisopropylamide × 2HCl                                                                   H--Arg--ANBA--Ile diisopropylamide × 2HCl        132                                                                               H--Gly--Val--Arg--ANBA--Ile                                                                         Z--Gly--Val--OH           6, 7b                           dicyclohexylamide × 2HCl                                                                      H--Arg--ANBA--Ile dicyclohexylamide × 2HCl       133                                                                               H--D-Phe--Pro--Arg--ANBA--Arg                                                                       Boc--D-Phe--Pro--OH       6, 7c                           isopropylamide × 3HCl                                                                         H--Arg--ANBA--Arg(NO.sub.2) isopropylamide                                     × 2HCl                                           134                                                                               H--D-Phe--Pip--Arg--ANBA--Arg                                                                       Boc--D-Phe--Pip--OH       6, 7c                           isopropylamide × 3HCl                                                                         H--Arg--ANBA--Arg(NO.sub.2) isopropylamide                                     ×  2HCl                                          __________________________________________________________________________

The Tables II to IX which follow show results from enzymatic measurements. These particularly show the advantage of the new compounds compared with those of the state of the art.

The concentrations indicated for the enzymes relate to the stock solutions which were employed. In the test, these stock solutions were diluted in the ratio 1:10 with buffer. The pH of the buffer is that for optimum activity of the relevant enzyme.

All the enzymes employed, excepting trypsin, are products of Behringwerke AG. Trypsin is obtained from SERVA. "Activator" designates the 1:1 complex between human plasminogen and streptokinase.

                                      TABLE II                                     __________________________________________________________________________     Changes in specificity of the enzyme substrates as a function of the size      of the substituents R in the                                                   general formula I, using the example of H--D-Phe--Pro--Arg--ANBA ester,        in ΔOD/min at 405 nm.                                                    Synthetic substrate ×                                                                    Thrombin                                                                             Plasmin                                                                              Kallikrein                                                                             Urokinase                                                                            Trypsin                              2 HCl 3.0 mmol/l                                                                               6 IU/ml                                                                              2 CTA/ml                                                                             0.85 BAEE/ml                                                                           5000 IU/ml                                                                           1.4 γ/ml                       __________________________________________________________________________     H--D-Phe--Pro--Arg--ANBA                                                       methyl ester    0.335 0.200 0.230   0.090 0.160                                ethyl ester     0.360 0.180 0.180   0.070 0.110                                isopropyl ester 0.355 0.130 0.110   0.050 0.090                                n-butyl ester   0.365 0.100 0.095   0.050 0.080                                2-pentyl ester  0.340 0.080 0.060   0.030 0.050                                benzyl ester    0.350 0.025 0.035   0.015 0.035                                __________________________________________________________________________      While the sensitivity of the various peptideANBA esters towards thrombin       remains the same and is of an order of magnitude utilizable for enzymatic      measurements, the specificity of the individual enzyme substrates              increases markedly with the size of the alcohol residue.                 

                                      TABLE III                                    __________________________________________________________________________     Comparison of the rates of cleavage of various thrombin substrates, after      contact phase                                                                  activation of human citrated plasma, in ΔOD/min at 405 nm. The           cleavage                                                                       by thrombin is shown for comparison.                                           Synthetic substrate × 2 HCl                                                                      Plasma after contact                                                                      Thrombin                                    3 mmol/l                phase activation 10 μl                                                                 6 IU/ml                                     __________________________________________________________________________     Substrates for thrombin according                                              to the state of the art:                                                       H--D-CHA--But--Arg--pNA 0.325      0.300                                       H--D-Phe--Pro--Arg--pNA 0.100      0.350                                       H--D-Phe--Pip--Arg--pNA 0.090      0.350                                       Thrombin substr. according to the                                              invention:                                                                     H--D-Phe--Pro--Arg--ANBA isopropylamide                                                                0.037      0.350                                       H--D-Phe--Pro--Arg--ANBA--γ-But ethyl ester                                                      0.028      0.360                                       __________________________________________________________________________      When human citrated plasma is activated with dextran sulfate in the            absence of phospholipid and calcium, then, according to the present state      of knowledge, only the proteases Factor XII, Factor XI and plasma              kallikrein are activated. When commercially available thrombin substrates      are compared in this test system, with the thrombin substrates according       to the invention, it emerges that the substrates according to the state o      the art are cleaved at a rate which is a multiple of that for the new          substrates.                                                              

Tables IV to IX show comparisons of the rates fo cleavage by various proteolytic enzymes of substrates according to the state of the art and of some compounds according to the invention. The superiority of the enzyme substrates according to the invention is clear from these tables. Thus, the sensitivity of the individual substrates toward a given enzyme is adequate and is of the same order of magnitude as for the substrates of the state of the art. The insensitivity of the compounds according to the invention toward other proteases, which can likewise occur in the plasma, increases as a function of the type and size of the substituent in the peptide-ANBA derivatives. Thus errors of measurement in the enzymatic test are diminished or even eliminated when the new compounds are used.

                                      TABLE IV                                     __________________________________________________________________________     Rates of cleavage of some thrombin substrates according to the invention       in ΔOD/min at                                                            405 nm compared with substrates according to the state of the art.             Synthetic substrates    Activator                                                                             Thrombin                                                                             Plasmin                                                                              Kallikrein                                                                             F XII a                     3 mmol/l                2700 FU/ml                                                                            6 IU/ml                                                                              2 CTA/ml                                                                             0.85 BAEE/ml                                                                           3.6 IU/ml                   __________________________________________________________________________     Substrates for thrombin                                                        according to the state                                                         of the art:                                                                    Tos--Gly--Pro--Arg--pNA 0.260  0.430 0.460 0.240   0.180                       H--D-Phe--Pip--Arg--pNA 0.105  0.350 0.110 0.210   0.063                       H--D-Phe--Pro--Arg--pNA 0.115  0.350 0.230 0.220   0.068                       H--D-CHA--But--Arg--pNA 0.140  0.300 0.300 0.680   0.100                       Thrombin substrates accord-                                                    ing to the invention:                                                          H--D-Phe--Pro--Arg--2-methoxy-pNA                                                                      0.090  0.340 0.130 0.075   0.160                       H--D-Phe--Pro--Arg--ANBA                                                                               0.180  0.360 0.180 0.180   0.030                       ethyl ester                                                                    H--D-Phe--Pro--Arg--ANBA                                                                               0.090  0.350 0.045 0.020   0.012                       isopropylamide                                                                 H--D-Phe--Pro--Arg--ANBA--Ile--O--CH.sub.3                                                             0.060  0.360 0.040 0.030   0.011                       H--D-Phe--Pro--Arg--ANBA di-                                                                           0.070  0.345 0.020 0.015   0.010                       methylaminopropylamide                                                         H--D-Phe--Pro--Arg--ANBA--Ala                                                                          0.045  0.325 0.030 0.020   0.005                       isopropylamide                                                                 Tos--Gly--Pro--Arg--ANBA                                                                               0.090  0.320 0.120 0.040   0.020                       isopropylamide                                                                 __________________________________________________________________________

                                      TABLE V                                      __________________________________________________________________________     Rates of cleavage of some kallikrein substrates according to the               invention in ΔOD/min at                                                  405 nm compared with substrates according to the state of the art.             Synethetic substrates                                                                           Activator                                                                             Plasmin                                                                              Kallikrein                                                                             F XII A                                                                              α-chymotrypsin               3 mmol/l         2700 FU/ml                                                                            2 CTA/ml                                                                             0.85 BAEE/ml                                                                           3.6 IU/ml                                                                            2 mg/ml                            __________________________________________________________________________     Substrates for kalli-                                                          krein according to                                                             the state of the art:                                                          H--D-Pro--Phe--Arg--pNA                                                                         0.980  0.345 1.46    0.570 0.040                              Bz--Pro--Phe--Arg--pNA                                                                          0.110  0.055 0.450   0     0.010                              Kallikrein substrates                                                          according to the invention:                                                    H--D-Pro--Phe--Arg--2-methoxy-                                                                  0.480  0.125 1.00    0.186 0.010                              pNA                                                                            H--D-Pro--Phe--Arg--ANBA                                                                        0.380  0.145 1.20    0.200 0.030                              ethyl ester                                                                    H--D-Pro--Phe--Arg--ANBA                                                                        0.010  0.020 0.35    0.040 0.010                              neopentylamide                                                                 __________________________________________________________________________

                                      TABLE VI                                     __________________________________________________________________________     Rates of cleavage of some urokinase substrates according to the invention      in Δ OD/min at                                                           405 nm compared with substrates according to the state of the art.             Synthetic substrates                                                                            Activator                                                                             Urokinase                                                                            C1-Esterase                                                                           Trypsin                                                                             α-chymotrypsin                 3 mmol/l         2700 FU/ml                                                                            5000 IU/ml                                                                           160 U/ml                                                                              1.4 γ/ml                                                                      2 mg/ml                              __________________________________________________________________________     Substrates for urokinase                                                       according to the state                                                         of the art:                                                                    Pyr--Gly--Arg--pNA                                                                              0.115  0.175 0.080  0.255                                                                               0.230                                Urokinase substrates                                                           according to the                                                               invention:                                                                     Pyr--Gly--Arg--2-methoxy-pNA                                                                    0.110  0.205 0.065  0.090                                                                               0.040                                Pyr--Gly--Arg--ANBA                                                                             0.035  0.125 0.012  0.035                                                                               0.060                                isopropylamide                                                                 Pyr--Gly--Arg--ANBA                                                                             0.040  0.125 0.010  0.025                                                                               0.055                                benzylamide                                                                    Pyr--Gly--Arg--ANBA                                                                             0.070  0.165 0.015  0.220                                                                               0.095                                n-butyl ester                                                                  __________________________________________________________________________

                  TABLE VII                                                        ______________________________________                                         Rates of cleavage of some plasmin substrates according to the                  invention in ΔOD/min at 405 nm compared with substrates                  according to the state of the art.                                                              Plasmin  Activator                                                                               Kallikrein                                  Synthetic substrates                                                                            2        2700     0.85                                        3.0 mmol/l       CTA/ml   FU/ml    BAEE/ml                                     ______________________________________                                         Plasmin substrates accord-                                                     ing to the state of                                                            the art:                                                                       H--D-Val--Leu--Lys--pNA                                                                         0.180    0.320    0.060                                       H--D-Phe--Tyr--Arg--pNA                                                                         0.430    0.950    0.590                                       H--D-Phe--Tyr--Lys--pNA                                                                         0.210    0.350    0.100                                       Plasmin substrates accord-                                                     ing to the invention:                                                          H--D-Phe--Tyr--Lys--ANBA                                                                        0.165    0.155    0.010                                       isoproylamide                                                                  H--D-Val--Leu--Lys--ANBA                                                                        0.270    0.100    0.005                                       isopropylamide                                                                 ______________________________________                                          None of the substrates mentioned in this Table are cleaved by thrombin of      F XII a.                                                                 

                                      TABLE VIII                                   __________________________________________________________________________     Rates of cleavage of some Factor X a substrates according to the               invention                                                                      in ΔOD/min at 405 nm compared with substrates according to the           state of the art.                                                              Synthetic substrates                                                                          Plasmin                                                                              F X a Kallikrein                                                                             Urokinase                                                                            Trypsin                               3 mmol/l       2 CTA/ml                                                                             0.2 IU/ml                                                                            0.85 BAEE/ml                                                                           5000 IU/ml                                                                           1.4 γ/ml                        __________________________________________________________________________     Factor X a substrates accor-                                                   ding to the state of the                                                       art:                                                                           Bz--Ile--Glu(OMe)--Gly--                                                                      0.020 0.110 0.015   0.035 0.140                                 Arg--pNA                                                                       Z--D-Leu--Gly--Arg--pNA                                                                       0.210 0.250 0.148   0.178 0.093                                 Factor X a substrates accor-                                                   ding to the invention:                                                         Z--D-Leu--Gly--Arg--2-                                                                        0.162 0.410 0.067   0.108 0.048                                 methoxy-pNA                                                                    Z--D-Leu--Gly--Arg--ANBA                                                                      0.057 0.151 0.050   0.082 0.069                                 methylamide                                                                    Bz--Ile--Glu(OMe)--Gly--                                                                      0.001 0.085 0.001   0.080 0.040                                 Arg--ANBA methylamide                                                          __________________________________________________________________________

                  TABLE IX                                                         ______________________________________                                         Rate of cleavage of some C1-esterase substrates according to the               invention in ΔOD/min at 405 nm.                                          Synthetic substrates     C1-esterase                                           3 mmol/l                 160 U/ml                                              ______________________________________                                         Boc--Lys(Z)--Gly--Arg--2-methoxy-pNA                                                                    0.34                                                  H--Lys(Z)--Gly--Arg--2-methoxy-pNA                                                                      0.38                                                  H--Lys(Z)--Gly--Arg--2-butoxy-pNA                                                                       0.74                                                  H--Lys(Z)--Gly--Gly--Arg--2-methoxy-pNA                                                                 0.25                                                  H--D-Val--Leu--Arg--2-methoxy-pNA                                                                       0.54                                                  H--D-Val--Leu--Arg--2-butoxy-pNA                                                                        0.97                                                  ______________________________________                                    

PREPARATION OF THE NEW COMPOUNDS

All the individual reaction steps in the synthesis of the new compounds which are listed in Table I are carried out in a similar manner. A general description is given for each step in the synthesis.

1. Synthesis of the chromogenic ANBA ester (R COOR₁)

(a) 7.9 ml (0.11 mole) of thionyl chloride were added to 1 mole of the appropriate alcohol at -5° C. with exclusion of moisture. 18.2 g (0.1 mole) of ANBA were added to this solution at -5° C. After addition was complete, the mixture was slowly warmed to 50° C. and stirred at this temperature for 4 h. The solvent was removed by distillation in vacuo, and the oily residue was dissolved in chloroform. The organic phase was washed with 1M KHCO₃, water, 5% citric acid and again with water. It was dried over Na₂ SO₄. After filtration, the solvent was removed by distillation in vacuo. It was possible to recrystallize the product from a suitable solvent or to purify it by chromatography on silica gel. The yields were around 60 percent.

(b) Alcohols which have low reactivity towards thionyl chloride, such as aliphatic alcohols having 6 carbon atoms or more, or araliphatic alcohols having 7 carbon atoms or more, and alcohols which are solid under the reaction conditions described above, such as phenol or naphthol, were converted into the potassium salt. 0.1 mole of ANBA and 0.1 mole of HOBt were dissolved in 100 ml of DMF, and a solution of 0.1 mole of DCCI in 100 ml of DMF was added dropwise over the course of 30 min. After stirring at RT for 1 h, 0.1 mole of the appropriate potassium alcoholate was added and the mixture was stirred at RT for 16 h. Working up was carried out as above. The yields were around 40 percent.

2. Synthesis of the chromogenic ANBA amides (R CONR₂ R₃, CONH--(CH₂)_(n) --N(CH₃)₂, CO--Y--OR₁ or CO--Y--NR₂ R₃)

18.2 g (100 mmol) of 5-amino-2-nitrobenzoic acid (ANBA) and 15.3 g (100 mmol) of HOBt×H₂ O were dissolved in 100 ml of DMF, and a solution of 20.6 g (100 mmol) of DCCI in 100 ml of DMF was added dropwise over the course of 30 min. After stirring at RT for 1 h, 0.1 mole of the amine component was added. If the amine component was in the form of its salt, then 0.1 mole of NMM was also added. After stirring at RT for 16 h, precipitated DCH was filtered off and the solvent was removed in vacuo. The remaining oily residue was dissolved in EA and washed several times with 5% (w:v) citric acid, water, 1M KHCO₃ solution and water. After drying over Na₂ SO₄, the solvent was removed by distillation in vacuo. The crystalline product was recrystallized from a suitable solvent. The yields were around 80 to 90 percent.

3. Synthesis of the chromogenic 2-alkoxy-pNA derivatives (R OR₁)

7.7 g (50 mmol) of 2-amino-5-nitrophenol were dissolved in 100 ml of acetone, the apparatus was flushed with nitrogen and 7.0 g (50 mmol) of K₂ CO₃ and 50 mmol of alkyl bromide were added. The mixture was boiled under reflux, with stirring for 8 h. After cooling to 0° C., it was filtered and the solvent was removed by distillation in vacuo. The residue was dissolved in ether and crystallized by addition of PE (40/60). The yields were about 50 percent.

4. Coupling of the chromogenic components

50 mmol of N.sup.α, N^(G) -protected arginine or N.sup.α, N.sup.ω -protected lysine or ornithine, 50 mmol of chromogenic amine corresponding to 1, 2 or 3, and 6.8 g (100 mmol) of imidazole were dissolved in 250 ml of pyridine and the solution was cooled to -20° C. Then 7.5 ml (mmol) of POCl₃ were added dropwise while maintaining this temperature. After addition was complete, the mixture was allowed to warm slowly to RT. The solvent was removed in vacuo and the resulting oil was taken up in 1M KHCO₃. The aqueous phase was extracted three times with EA. The organic phase was washed with 1M KHCO₃ solution, water, 5% citric acid and again with water and dried over Na₂ SO₄. After filtration, the solvent was removed by distillation and the residue was triturated with ether. The yields were around 40 to 60 percent.

5. Splittng off the protective groups

(a) Splitting off the benzyloxycarbonyl group (Z)

10 mmol of protected, chromogenic amino acid derivative according to 4. were dissolved in 20 ml of HAc, and 30 ml of 33% HBr in HAc was added at RT with exclusion of moisture. After stirring at RT for 40 min., the solvent was evaporated in vacuo and the product was triturated with ether. After washing several times with ether, the substance was dried in vacuo over solid KOH for 20 h. The yields were around 90 percent.

(b) Splitting off the t-butyloxycarbonyl group (Boc)

10 mmol of protected, chromogenic amino acid derivative according to 4. were dissolved in 50 ml of 1.2N HCl in HAc and stirred at RT for 20 min. The solvent was removed in vacuo and the product was triturated with ether. After washing several times with ether, the substance is dried in vacuo over solid KOH for 20 h. The yields were around 95 percent.

6. Coupling reaction

5 mmol of protected dipeptide or tripeptide derivative, the terminal carboxyl group of which is unsubstituted, were dissolved in 20 ml of DMF, and 5 mmol of DCCI and 5 mmmol of HOBt were added at 0° C. After stirring at 0° C. for 30 min., the mixture was warmed to RT and 5 mmol of chromogenic amino acid derivative according to 5a or 5b and 5.5 mmmol of NMM were added. After stirring at RT for 16 h, the DCH was removed by filtration and the solvent was evaporated in vacuo. The yellow residue was dissolved in MeOH and chromatographed on a Sephadex®LH 20 column. The fractions containing the pure substance were combined and the solvent was removed in vacuo. The amorphous solid obtained was washed several times with ether and dried in vacuo over P₄ O₁₀. The yields were around 70 percent.

7. Splitting off the protective groups

(a) Splitting off the t-butyloxycarbonyl group (Boc) and, where appropriate, the t-butyl ester group in the side chain of GLu and Asp.

2 mmol of protected, chromogenic peptide derivative were dissolved in 30 ml of 1.2N HCl/HAc and stirred at RT for 20 min. The solvent was removed in vacuo and the product was triturated with ether. After washing several times with ether, the substance was dried over solid KOH under high vacuum.

(b) Splitting off the benzyloxycarbonyl group (Z)

2 mmol of protected, chromogenic peptide derivative were dissolved in 10 ml of HAc, and 15 ml of 33% HBr in HAc were added at RT with exclusion of moisture. After stirring at RT for 1 h, the solvent was evaporated in vacuo and the product was triturated with ether. After washing several times with ether, the substance was dissolved in water, converted into the hydrochloride using an ion exchanger, and freeze-dried.

(c) Splitting off all protective groups

2 mmol of the protected, chromogenic peptide derivative are dissolved in 10 ml of HF in the presence of 1.0 ml of anisole and stirred at 0° C. for 1 h. The HF is removed in a stream of dry nitrogen and the substance is dried over solid KOH under high vacuum. The product was washed several times with ether, dissolved in water, converted into the hydrochloride using an ion exchanger, and freeze-dried.

Examples for the use of the new compounds for determination of enzymes and inhibitors:

EXAMPLE 1 Thrombin determination

Substrate: H-D-Phe-Pro-Arg-ANBA neopentylamide

Test mixture:

20 μl of plasma which had been previously diluted 1:51 with physiologic NaCl were incubated with 500 μl of activating reagent (see below) at 37° C. for 4 min. Then 100 μl of substrate solution (3 mmol/l) were added, and the ΔE/min at 405 nm was determined in a photometer. The standard used was a reference curve with standard human plasma.

Activating reagent:

PTT reagent (reagent for determining the partial thromboplastin time) of Behringwerke was dissolved, according to the instructions, in distilled water and diluted 1:4 with a solution containing 50 ug/ml of RVV (russell viper venom, Sigma); 50 mmol/l of tris; 75 mmol/l of NaCl; 7.5 mmol/l of Ca²⁺ and 0.1 g/100 ml of human albumin.

EXAMPLE 2 Antithrombin III determination

Substrate: H-D-Phe-Pro-Arg-ANBA-Ile methyl ester

Test mixture:

50 μl of plasma which had previously been diluted 1:51 with physiologic NaCl was preincubated with 1.0 ml of a human α-thrombin solution (0.3 IU/ml; 100 mmol/l of tris; 100 mmol/l of NaCl, pH=8.2) at 37° C. for 5 min. Then 100 μl of substrate solution (2 mmol/l) were added, and ΔE/min at 405 nm was determined in a photometer.

The standard used was a reference curve with standard human plasma.

EXAMPLE 3 Plasminogen determination

Substrate: H-D-Val-Leu-Lys-ANBA methyl ester

Test mixture:

20 μl of plasma were incubated with 1.0 ml of streptokinase reagent (1,000 Fibr. U/ml; 100 mmol/l of KH₂ PO₄ ; 100 mmol/l of NaCl; pH=7.2) at 37° C. for 10 min. Then 100 μl of substrate reagent (3 mmol/l) were added and ΔE/min at 405 nm was determined in a photometer.

The standard used was a reference curve with standard human plasma.

EXAMPLE 4 α₂ -antiplasmin determination

Substrate: H-D-Val-Leu-Lys-ANBA methylamide

Test mixture:

(a) 20 μl of plasma were preincubated with 1.0 ml of plasmin (human) reagent (0.1 CTA-U/ml; 100 mmol/l of KH₂ PO₄ ; 150 mmol/l of NaCl; 25% glycerol, pH=7.2) at 37° C. for 1 min. Then 100 μl of substrate reagent (3 mmol/l) were added and ΔE/min at 405 nm was determined in a photometer.

The standard used was a reference curve with standard human plasma.

(b) 20 μl of plasma were mixed with 1.0 ml of substrate reagent (0.3 mmol/l; 100 mmol/l of KH₂ PO₄ ; 140 mmol/1 of NaCl, pH=7.2) and 100 μl of plasmin reagent (1 CTA-U/ml; 25-50% glycerol; 2 mmol/l of HCl, pH=2.5) at 37° C. ΔE/min was determined after 1 min.

The standard used was a reference curve with standard human plasma.

EXAMPLE 5 Factor Xa determination

Substrate: Z-D-Leu-Gly-Arg-2-methoxy-pNA

Test mixture:

20 μl of plasm were preincubated with 1 ml of activating reagent at 37° C. for 1 min. Then 100 μl of substrate reagent (3 mmol/l) were added and ΔE/min was determined. The standard used was a reference curve with standard human plasma.

Activating reagent:

25 ug of RVV/ml (russell viper venom, sigma); 50 mmol/l of tris; 25 mmol/l of CaCl₂ ; 200 mmol/l of NaCl, pH=8.3.

EXAMPLE 6 Prekallikrein determination

Substrate: H-D-Pro-Phe-Arg-ANBA isopropylamide

Test mixture:

10 μl of plasma were incubated with 1 ml of activating reagent at 37° C. for 1 min. Then 100 μl of substrate reagent (3 mmol/l) were added and ΔE/min was determined.

The standard used was a reference curve with standard human plasma.

Activating reagent:

Visually clear PTT reagent of the Behringwerke was dissolved, according to the instructions, in distilled water and diluted 1:6 with distilled water. A further 1:9 dilution was carried out with 50 mmol/l of tris, 12 mmol/l of NaCl, pH=7.8.

EXAMPLE 7 Urokinase determination

Substrate: Pyr-Gly-Arg-ANBA benzylamide

Test mixture:

1 ml of triethanolamine buffer (0.1 mole/l of TEA; 0.2 mmol/l of NaCl, pH=8.4) and 1 ml of substrate reagent (2 mmol/l) were added to 10 μl of urokinase (100-3,000 IU/ml) at 37° C., and then ΔE/min was determined.

Evaluation was assisted by a reference curve.

Determination of urokinase in urine

500 μl of triethanolamine buffer (0.5 mmol/l of TEA; 1 mole/l of NaCl, pH=8.4) and 0.1 ml of substrate reagent (2 mmol/l) were added to 500 μl of urine at 37° C., and ΔE/min was determined. Evaluation was assisted by a reference curve.

EXAMPLE 8 C1-inactivator determination

Substrate: H-D-Val-Leu-Arg-2-butoxy-pNA

Test mixture:

20 μl of plasma were incubated with 1 ml of C1-esterase reagent (10 mU/ml; 100 mmol/l of NaH₂ PO₄ ; 0.05% NaN₃ ; 0.2% Haemaccel; pH=7.5) at 30° C. for 15 min. Then 100 μl of substrate reagent (6 mmol/l) were added and ΔE/min at 405 nm was determined in a photometer. The standard used was a reference curve with standard human plasma. 

We claim:
 1. A method for the detection and determination of an endoprotease, comprising adding a compound of the formula I ##STR5## in which X denotes a hydrogen atom, a protective group customarily used in peptide chemistry or a group which irreversibly blocks the terminal amino group,A denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Pyr, Thr, Tyr and Val, C denotes a bond or an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asp, Glu, Gly, Leu, Lys, Ser and Val, D denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asp, Glu, Gly, His, Leu, Phe, Pip, Pro, Ser, Thr, Tyr and Val, B denotes L-arginine, L-homoarginine, L-Lysine, L-homolysine, L-ornithine or L-histidine, and R denotes COOR₁, CONR₂ R₃, CONH--(CH₂)_(n) --N(CH₃)₂, CO--Y--OR₁ and CO--Y--NR₂ R₃ in the 3-position or OR₁ in the 2-position of the 4-nitroaniline, in which R₁ denotes an aliphatic hydrocarbon radical having 1 to 6 carbon atoms, an aromatic hydrocarbon radical having 6 to 10 carbon atoms, an araliphatic hydrocarbon radical haing 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms. R₂ denotes a hydrogen atom or a radical defined under R₁, R₃ denotes an aliphatic hydrocarbon radical having 1 to 10 carbon atoms, an aromatic hydrocarbon radical having 6 to 10 carbon atoms, an araliphatic hydrocarbon radical having 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms, Y denotes an alpha-, beta- or gamma-amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asn, Asp, β-Ala, γ-But, Cys, Glu, Gly, Ile, Leu, Lys, Met, Arg, Phe, Pro, Ser, Thr, Tyr and Val, and n denotes 1 to 10, or its acid addition salts to a solution containing the endoprotease to be detected and determined, and measuring the amount of nitroaniline derivative produced, wherein the amount of the production of nitroaniline derivative is an indication of the activity of said endoprotease.
 2. A method for the detection and determination of an endoprotease, comprising adding a compound of the formula I ##STR6## in which X denotes a hydrogen atom, a protective group customarily used in peptide chemistry or a group which irreversibly blocks the terminal amino group,A denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Cys, Glu, Gln, Gly, His, Ile, Leu, Lys, Phe, Pro, Pyr, Thr, Tyr and Val, C denotes a bond or an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asp, Glu, Gly, Leu, Lys, Ser and Val, D denotes an amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asp, Glu, Gly, His, Leu, Phe, Pip, Pro, Ser, Thr, Tyr and Val, B denotes L-arginine, L-homoarginine, L-Lysine, L-homolysine, L-ornithine or L-histidine, and R denotes COOR₁, CONR₂ R³, CONH--(CH₂)_(n) --N(CH₃)₂, CO--Y--OR₁ and CO--Y--NR₂ R₃ in the 3-position or OR₁ in the 2-position of the 4-nitroaniline, in which R₁ denotes an aliphatic hydrocarbon radical having 1 to 6 carbon atoms, an aromatic hydrocarbon radical having 6 to 10 carbon atoms, an araliphatic hydrocarbon radical having 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms, R₂ denotes a hydrogen atom or a radical defined under R₁, R₃ denotes an aliphatic hydrocarbon radical having 1 to 10 carbon atoms, an aromatic hydrocarbon radical having 6 to 10 carbon atoms, an araliphatic hydrocarbon radical having 7 to 11 carbon atoms or an alicyclic hydrocarbon radical having 3 to 8 carbon atoms, Y denotes an alpha-, beta- or gamma-amino acid, the side-chain group of which can be unsubstituted or substituted, selected from the group consisting of Ala, Asn, Asp, β-Ala, γ-But, Cys, Glu, Gly, Ile, Leu, Lys, Met, Arg, Phe, Pro, Ser, Thr, Tyr and Val, and n denotes 1 to 10, or its acid addition salts to a solution containing the endoprotease to be detected and determined, and measuring the rate at which the nitroaniline derivative is produced, wherein the rate of production of the nitroaniline derivative is an indication of the activity of said endoprotease. 